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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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which, at first descends steeply and afterwards more gently. The habit of the lowland lying between the glacier and the ocean indicates that it is built of morainic material. Near the sea is a belt of timber, but this is separated from the ice by a barren tract similar to that about Davidson Glacier. A barren zone several hundred yards broad is seen to flank the glacier on the southwest, and a similar zone borders its companion Crescent Glacier. These features doubtless indicate shrinking in modern times, the change having been of moderate amount, although greater than in the case of LaPerouse and Columbia^ Glaciers. The Crescent is comparatively narrow, and approaches the sea with a higher grade. A curve in its trough conceals its upper course."
When we saw it in 1910 (PI. CXXIV, B) Amherst Glacier was little crevassed and had a broad belt of ablation moraine upon the terminus, no changes being detected by comparison with Merriam's 1899 photograph. The Crescent Glacier also seemed unchanged, and from a distance no signs of unusual activity were seen in Williams, Dartmouth, and Tommy Glaciers. Cap Glacier is typical of many nev6 fields upon mountain slopes, being thin, severely crevassed, and intermediate in character between the snow-field and the valley glacier, though most resembling the former.
Glacial Erosion—Features above Sea Level. Glacial erosion has had a profound influence in producing the present straight, steep-walled depression of College Fiord. Evidence of glacial erosion in the form of striae on rock ledges, in roches moutonnees forms, in the absence of spurs on the valley walls, and in the oversteepened lower portion of the fiord walls is everywhere apparent. There are also cirques of various sizes, a large number of them containing small glaciers, as between Vassar and Bryn Mawr Glaciers, between Baltimore and Radcliffe Glaciers, etc.
There are many differences in the degree of glacial erosion, judging from the valley-wall features. For example, the south side of Cresent Glacier valley shows an undercut cliflE, evidently due to long-continued glacial erosion on the outer side of a curve, as in a river. The eastern wall of College Fiord, especially between College Point and Downer Glacier, and just north of Coghill River, is remarkable for irregularities above sea level in contrast with the smoother western side. The eastern side has many uneroded spurs, irregular hummocks and reefs; the western is remarkable for its smoothness and simplicity of contour, for its many roches moutonne'es with striae and glacial grooves parallel to the trend of the fiord, and for the bare, smoothed, nearly horizontal rock ledges high upon the fiord wall. North of College Point the expanded Harvard Glacier seems to have hugged the western shore and to have eroded here more efficiently, despite the presence of many tributaries from the west whose thrust would tend to push the glacier over toward the eastern side. But it is very probable that the expanded Yale Glacier swept over College Point and by its great volume overcame the influence of this thrust.
There are many hanging valleys above sea level (h, PI. CXXVI) and as Gilbert has already noted, the cascading glaciers on the western side of the fiord descend out of hanging valleys. There are also hanging valleys out of which the glaciers do not now cascade. The ascending altitudes of these hanging valleys, whose levels as measured in 1910 agree except in minor particulars with Gilbert's computations in 1899, and the fact that there are two steps, as noted by Gannett, have been explained by Gilbert,1 as follows, the relationships being shown in Fig. 41.
i Gilbert, G. K., Harriman Alaska Expedition, Vol. 3, 1904, pp. 175-176.